Initial developmental studies in monkeys showed that d-amphetamine-induced displacement of the radiotracer was dependent upon the release of endogenous dopamine and could be blocked by pretreatment with reserpin (which depletes dopamine) or alpha-methyl-paratyrosine (which inhibits dopamine synthesis. We reported the extension of this paradigm to healthy human subjects. Injection of d-amphetamine (20 mg i.v.bolus) induced displacement of [123I]IBMZ from the striatum, and the amount of displacement was correlated with pyschological measures of activation.